Synthesis Of Transition Metal And Heteroatom Co-doped Nanocarbons And Their Application In Oxygen Electroreduction

Due to the rapid development of economy and the explosive growth of population,the demand for energy is drastically increasing.Nowadays,the commonly used energy sources are fossil fuels such as oil,natural gas and coal.However,the reserve of fossil fuels in earth crust is very limited,and excessive use of fossil energy can cause serious environmental problems,such as haze,greenhouse effect,etc.,which and seriously affects people’s health and living environment.Developing efficient energy storage and conversion devices is one of the effective ways to solve the afore-mentioned problems.Due to the high energy conversion efficiency,proton exchange membrane fuel cell（PEMFC）,a novel type of energy conversion device that can directly convert the the chemical energy in fuels to electricity,has attracted intensive research attentions all over the world.However,the performance and lifetime this kind of fuel cell are predominantely determined by the slow kinetics of cathode oxygen reduction reaction（ORR）.At present,platinum（Pt）is the universal choice of catalyst for ORR.Nevertheless,Pt is a precious metal,its high cost,scarcity as well as other serious problems encountered in working such as agglomeration and weak immunity to CO poisoning,hinder its widespread application for the large-scale commercialization of fuel cell technology.Therefore,exploration of low-cost candidates to traditional commercial Pt catalysts is highly demanded.In this thesis,a series of low-cost and of catalysts with high ORR catalytic activity were prepared through a simple and effective way.The structure,morphology and compositions of thus-synthesized samples were carefully analyzed,and their correlations with the ORR catalytic activities were also disclosed.The outcomes of present work may help better understand the catalytic mechanism on transitions metal and nitrogen codoped carbons,and boost the design and synghesis of more efficient catalysts with resemble structures.The main contents of this thesis are listed as follows:Metallic FeCo alloy encapsulated in N,S-codoped carbon nanotubes（FeCo@N,S-CNT）was prepared via pyrolyzing the hybrid of Fe-and Co-containing Prussian blue analogues（PBA）and trithinocyanuric acid.Electrochemical measurements reveale that the sample pyrolyzed at 800℃displayed the best ORR activity among the series.The superior electrocatalytic activities of FeCo@N,S-CNT-800 catalysts is most likely contributed by the following factors:The good conductivityof one one-dimensional（1D）nanocarbon is beneficial to the transmission of electrons;A large specific surface area with abundant mesoporous strctures helps expose more active sites and facilitate mass transport;The synergistic effect between FeCo alloy and the wall of carbon tubes;S-doping can further introduce defects onto the carbon substrate and correspondingly change the electron distribution on carbon substrate,which is good for the adsorption of oxygen.The Co nanoparticles embedded into 2D nitrogen-doped graphene（Co@NG）for ORR were prepared by using graphene oxide,graphite-carbon nitride（g-C₃N₄）and cobalt prussian blue（PB）as precursors with the presence of SiO₂ nanoparticle templates,and they were found to exhibit excellent ORR performance.Due to the presence of SiO₂ template,the specific surface area of the catalyst is about 703.26 m²/g,and the pore size is concentrated in the mesoporous region.In 0.1M KOH solution,the ORR catalytic performance of the catalyst was highly comparable to that of commercial Pt catalyst.Moreover,it also displayed good activity for hydrogen evolution reaction（HER）,with an onset potentialof about-50mV,and and overpotential at 10mA/cm² of 180mV.Thesuperiorious ORR and HER activity can be attributed to the 2D structure,larger specific surface,excellent pore size distribution and the presence of high density of Co-N_x structures.